1. Field of the Invention
The present invention relates to a timepiece movement and, more particularly, to a timepiece movement in which a minute wheel and a second wheel are independently rotated and a standard position thereof can be detected.
2. Background Information
Conventionally, there is known a timepiece movement which is provided with a driving gear train for a second wheel and a driving gear train for a minute wheel having an aperture and a shading portion in a light path disposed between a light emitting diode and a light-receiving sensor opposite the light emitting diode. The timepiece movement automatically performs an initial position detection operation by driving the above gear trains in a state in which the light emitting diode is operated so as to detect a position in which an output of the light-receiving sensor is inverted from a level 0 to a level 1, and the determined position is set as an initial position of the second wheel, the minute wheel and an hour wheel.
In the foregoing conventional timepiece movement, a driving motor for driving the second wheel and a driving motor for driving the minute wheel and the hour wheel are provided, and a photo-diode or a photo-transistor is used as the light-receiving sensor. The driving motors for the second wheel and the hour and minute wheels are alternately rotated so that, at first, apertures of the second wheel and the hour and minute wheels coincide with each other so as to invert the output of the light-receiving sensor to the level 1, and thereafter the initial position detection operation is performed.
However, since there are a great number of combinations for which the aperture of the second wheel and the aperture of the hour and minute wheels coincide, there is a problem that a lot of time is necessary for bringing these apertures to coincide with each other. Further, the construction of the timepiece movement is such that most of the portions of the gears of the gear trains of the second wheel and the hour and minute wheels are defined by the apertures, thereby increasing a probability that infrared rays of the light emitting diode are transmitted therethrough. By this construction, the portions defined by the aperture hardly serve for detecting the position of the hour and minute wheels so that a time for detecting the position thereof increases. Further, since most of the portions of the gears are defined by the apertures, the strength thereof is greatly reduced.